Cell processing includes steps where cells or cell elements are treated with different process chemicals or are washed and then separated from a liquid phase. For example, when preparing frozen erythrocytes for transfusion, erythrocytes are separated from cryopreservatives and other blood components such as white cells, platelets and sub-cellular debris. The entire process must be performed under sterile conditions that minimize the risk of contamination. Furthermore, whole blood is separated into its various therapeutic components such as red blood cells, white blood cells, platelets and plasma which are later transfused. There are different cell processing systems that process biological cells in an automated or semi-automated way. These systems may use a controller connected to various sensors and valves for controlling the process and helping an operator to maximize the processing efficiency. However, these systems do not interactively adjust the process based on the amount or type of the processed cells or different processing conditions.
During the separation, for example, by expression of the processing fluid, it is desirable to accurately differentiate the supernatant (for example, a wash solution) from the harvested cells in order to avoid losing valuable cellular product into the expressed (and thereafter discarded) wash solution. Various optical detectors have been designed and described in the prior art. However, there are several features that needed to be resolved. For example, the means and location of the optic assembly housing can be problematic. A separate plastic cuvette is typically used to provide flat, parallel surfaces through which the object cells must pass. These flat surfaces minimize optical distortion but add a separate object, the cuvette, to the disposable set designed to contain the cells and washing reagents. This additional cuvette increases the complexity and requires an extra operator step during set up of the instrument, as this cuvette must be accurately positioned in the optical detector housing. Any operator interaction may potentially introduce an error. If the housing is located away from the centrifuge, such design leaves a length of tubing between its location and the centrifuge that is full of packed cells immediately after the first of the cells have been detected. These cells are typically lost to the waste supernatant of the next wash cycle. Finally, cell processing may involve separating one cell type from another (e.g., the buffy coat containing white blood cells and platelets must be separated from erythrocytes being prepared as packed red cells for transfusion; erythrocytes must be removed from bone marrow during the preparation of progenitor cells).
Therefore, there is a need for an optical sensor for use in an automated interactive cell processing system. Such optical sensor would need to have a practical design and would need to provide precise and reproducible data for different disposable elements, varying amounts of processed cells, different types of processed cells, or different operators and processing laboratories.